Filtration devices comprising a plurality of discrete filter layers are well-known. Several varieties exist.
The filtration devices of interest to the present invention are those wherein several filter layers are arranged in a stack or bank within a common housing, such that fluid brought into the housing (i.e., through an inlet) passes through each filter layer sequentially prior to being released from said housing (i.e., through an outlet). Such “serial-flow” filtration devices may include other components, independent of the filter layers, that assist or have an influence on the flow path of fluid within the housing.
According to a common configuration, the filter layers in the filtration device are stacked such that the retentiveness of the constituent layers define a gradient from low to high. In such gradient filter devices, the foremost filter layer—i.e., the layer first impinged upon by fluid introduced into the housing—typically has the lowest retentiveness, whereas the subsequent layers are sequentially more retentive. In another common configuration, the retentiveness of each constituent filter layer is essentially the same, the layers typically being arranged with an eye towards the efficient use of a tight and limited space.
Serial-flow filtration devices are employed for various applications. Types of industrial applications include, for example, pharmaceutical manufacture, processing blood plasma or serum fractionation products, ophthalmic solution manufacture, the manufacture of specialty chemicals, and the like. In industrial applications, the filtration devices are typically configured for so-called “primary or secondary clarification”, i.e., the initial filtration of a fluid prior to further downstream cleaning and polishing processes. In such applications, the fluid is often handled in large batches (e.g., in the order of several thousands of liters) and typically has high solid content.
A key concern in the conduct of serial filtration is pressure management. As fluid enters the device, solids will generally be retained and accumulated more so on the foremost filter layer. Unchecked sedimentation on a filter layer will eventually give rise to so-called “cake” formation. This and like formations effectively decrease the porosity of the filter medium (cf., clogging), such that—given constant flow of fluid into the housing—upstream pressure will rise. If pressure reaches a certain level, the filtration process will either have to be terminated, for example, to replace, clean, or revitalize the “spent” filter layer. Otherwise, one risks catastrophic filter component failure and/or otherwise compromises or ruins one's filtration product or result.
When the filtration process is terminated, labor, time, and material resources (e.g., replacement components, cleaning fluids, etc.) need to be expended. Of particular note, in respect of labor, is the rather onerous task of disassembling and reassembling an industrial-sized filtration device. Stacks of large filter components when soaked with fluid are quite heavy, unwieldy, and often messy. Reducing the frequency with which such maintenance has long been and continues to be highly desirable.
In light of the above, for filtration devices employing serially-arranged filter layers, a need exists for automatically passing a clogged or otherwise spent filter layer at a prescribed pressure differential thereacross in a manner that is reasonably reliable and not inordinately expensive to implement.